Fluidized bed type reduction apparatus for iron ore particles and method for reducing iron ore particles using the apparatus

ABSTRACT

A reduction apparatus and a method for efficient reduction of fine iron ores of wide grain range comprising serially arranged a drying/preheating furnace, a first reducing furnace for prereduction and a second reduction furnace for final reduction, each working with bubbling fluidized bed and being connected each to a cyclone for capturing iron ore dust contained in the exhaust gases, having each a tapered shape smoothly expanded outwards and thus considerably decreasing elutriation of fine particles, increasing the reduction efficiency and enhancing the utilization of the reducing gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluidized-bed-type reductionapparatus for reducing fine iron ores in the procedure of producing pigiron or ingot iron and a method for reducing iron ore particles usingsuch an apparatus, and more particularly to a fluidized bed typereduction apparatus capable of efficiently reducing fine iron ores ofwide size ranges in a stably fluidized state and a method for reducingiron fine ores using the apparatus.

2. Description of the Prior Art

Generally, conventional methods for producing pig iron from reduced ironores include a method using blast furnaces and a method using shaftfurnaces. In the latter method, iron ores reduced in a shaft furnace aremelted in an electric furnace.

In the case of the method for producing pig iron using blast furnaces, alarge amount of coke is used as a heat source and reducing agent. Inaccordance with this method, iron ores are charged in the form ofsintered ores in order to improve the gas-permeability and reduction. Tothis end, conventional methods using blast furnaces need a coke oven forproducing coking coal and equipment for producing sintered ores. Forthis reason, the method using blast furnaces is a method requiring ahuge investment and a high energy consumption. Since high quality cokingcoal is maldistributed in the world and the amount of its reserves arediminishing, the shortage thereof becomes severe as the demand for steelincreases. On the other hand, the method of reducing iron ores usingshaft furnaces requires a pretreating step for pelletizing iron ores.Since this method also uses natural gas as a heat source and reducingagent, it has a drawback that it can be commercially implemented only inareas where an easy supply of natural gas is ensured.

Recently, a smelting reduction method capable of producing ingot ironfrom iron ores using non-coking coal in place of coke has beenremarkable as a new iron production method.

Such a smelting reduction method typically employs a system wherein ironores pre-reduced in a separate furnace are completely reduced in amelting furnace to produce hot metal. In the reduction furnace, ironores are reduced in a solid phase before they are melted. In otherwords, iron ores charged in the reduction furnace are reduced whilebeing in contact with hot reducing gas generated in the melting furnace.

The reduction process used in this method is classified into a movingbed type and a fluidized bed type in accordance with the condition thatiron ores are in contact with the reducing gas. It has been known thatone of the most promising method for the reduction of fine iron ores ofwide size distribution is the fluidized bed type process wherein theores are reduced in a fluidized state by a reducing gas supplied througha distributor which is installed in the lower part of the reactor.

An example of the fluidized-bed-type reduction furnace is disclosed inJapanese Patent Laid-open Publication No. Heisei 3-215621. As shown inFIG. 1, this furnace comprises a cylindrical reduction furnace 91 and acyclone 95. When iron ores are charged through an inlet 92 and areducing gas is supplied in the reduction furnace 91 via a line 93 and adistributor 96 at an appropriate flow rate, the iron ores form-afluidized bed above the distributor so that they can be mixed andagitated with the reducing gas. In this state, the iron ores can bereduced by the reducing gas. The reducing gas supplied in the furnaceforms bubbles in a layer of iron ore particles as if a fluid is boiled,and then rises through the particle layer, thereby forming a fluidizedbed of iron ore particles. Therefore, this fluidized bed is a bubblingfluidized bed. The reduced iron ores are discharged out of the reductionfurnace 91 through an outlet 94.

In the case of the fluidized-bed-type reduction apparatus disclosed inthe above publication, it is necessary to minimize the flow rate of thereducing gas while forming an effective fluidized bed so as not only toreduce the elutriation of iron ores, but also to increase the efficiencyof the reducing gas. To this end, the grain size of iron ore particlesshould be strictly limited to a certain range if the flow rate of thereducing gas in the fluidized bed is constant along the longitudinalaxis of the fluidized bed. In other words, the gas velocity of thereducing gas required to form an effective fluidized bed should becontrolled between a minimum fluidizing velocity and a terminalvelocity. For such a fluidized bed type reduction furnace, accordingly,iron ore particles should be screened in terms of their grain size sothat only those of similar grain ranges can be charged into thereduction furnace. If the operation is carried out at a high gasvelocity which is required to fluidize coarse iron ore (which would notbe fluidized at a low gas velocity), it will result in a large amount ofthe elutriation of fine iron ore because the terminal velocity of thefine ore is lower than the operating gas velocity. As the result, thedust collecting efficiency of the cyclones is reduced, therebyincreasing the loss of the raw material. Furthermore, the reduction rateof circulating fine iron ore is degraded because their mean residencetime in the reduction furnace is shorter than that of coarse iron ore.

The inventors proposed the present invention which can solve theabove-mentioned problems encountered in the conventional methods, basedon the results of their research and experiments.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a fluidized-bed-typereduction apparatus and a method for reducing fine iron ores using theapparatus, which can efficiently reduce fine iron ores of wide sizeranges in a stably fluidized state, thereby considerably decreasing theelutriation of the particles, increasing the reduction rate andenhancing the efficiency of the reducing gas.

In accordance with this object, an apparatus comprisingserially-arranged, multi-stage fluidized bed type furnaces is provided.In this system, each reactor is in tapered shape, i.e., the diameter ofthe reactor increases in the upper direction in order to stably fluidizefine iron ore of wide grain size ranges. The reduction apparatusincludes a furnace for drying and preheating fine iron ore particlesand, at least, one reduction furnace for reducing the dried/preheatediron ores.

In accordance with one aspect, the present invention provides afluidized-bed-type reduction apparatus for reducing fine iron ores,comprising: a drying/preheating furnace for drying and preheating ironores supplied from a hopper in a bubbling fluidized state; a firstcyclone for capturing dusty iron ores contained in exhaust gas from thedrying/preheating furnace; a reduction furnace for finally reducing thedried/preheated iron ores in a bubbling fluidized state; and a secondcyclone for collecting dusty iron ores contained in exhaust gas from thereduction furnace. Hereinafter, this apparatus will be referred to as atwo-stage fluidized-bed-type reduction apparatus.

In accordance with another aspect, the present invention provides afluidized-bed-type reduction apparatus for reducing fine iron ore,comprising: a drying/preheating furnace for drying and preheating fineiron ores supplied from a hopper, in a bubbling fluidized state; a firstcyclone for capturing dusty iron ores contained in exhaust gas from thedrying/preheating furnace; a first reduction furnace pre-reducing thedried/preheated iron ores in a bubbling fluidized state; a secondcyclone for collecting dusty iron ores contained in exhaust gas from thefirst reduction furnace; a second reduction furnace for finally reducingthe pre-reduced iron ores in a bubbling fluidized state; and a thirdcyclone for capturing dusty iron ores contained in exhaust gas from thesecond reduction furnace. Hereinafter, this apparatus will be referredto as a three-stage fluidized bed type reduction apparatus.

In accordance with another aspect, the present invention provides amethod for reducing fine iron ores of wide size distribution, comprisingthe steps of: drying and preheating the iron ores in a bubblingfluidized state in a tapered-fluidized bed of which diameter increasesin the upper direction; and finally reducing the dried/preheated ironores in a bubbling fluidized state in a tapered-fluidized bed of whichdiameter increases in the upper direction. Hereinafter, this method willbe referred to as a two-stage reduction method.

In accordance with another aspect, the present invention provides amethod for reducing fine iron ores of wide size distribution, comprisingthe steps of: drying and preheating the iron ores in a bubblingfluidized state in a tapered-fluidized bed of which diameter increasesin the upper direction; pre-reducing the dried/preheated iron ores in abubbling fluidized state in a first tapered-fluidized bed of whichdiamer increases in the upper direction; and finally reducing thepre-reduced iron ores in a bubbling fluidized state in a secondtapered-fluidized bed of which diameter increases in the upperdirection. Hereinafter, this method will be referred to as a three-stagereduction method.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the invention will become apparent from thefollowing description of embodiments in conjunction with theaccompanying drawings in which:

FIG. 1 is a schematic diagram illustrating a conventionalfluidized-bed-type reduction furnace for reducing iron ores; and

FIG. 2 is a schematic diagram illustrating a fluidized-bed typereduction apparatus for reducing fine iron ores in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 2, a three-stage fluidized-bed-type reduction apparatus forreducing fine iron ores of wide size distribution in accordance with thepresent invention is illustrated.

As shown in FIG. 2, the three-stage, fluidized-bed-type reductionapparatus 1 includes a furnace 10 for drying and preheating iron ores,which are supplied as a raw material from a hopper 70, in a bubblingfluidized state. A first cyclone 40, which serves to collect dusty ironores contained in exhaust gas discharged from the drying/preheatingfurnace 10, is connected to the above-mentioned drying/preheatingfurnace 10. Under the drying/preheating furnace 10, a first reductionfurnace 20 is arranged to receive the dried/preheated iron oresdischarged from the drying/preheating furnace 10. In the first reductionfurnace 20, the dried/pre-heated ores are pre-reduced in a bubblingfluidized state. A second cyclone 50 is connected to the first reductionfurnace 20 in order to collect dusty iron ores contained in exhaust gasdischarged from the first reduction furnace 20. A second reductionfurnace 30 is also arranged under the first reduction furnace 20. Thesecond reduction furnace 30 receives the pre-reduced iron ores from thefirst reduction furnace 20 and finally reduces the pre-heated iron oresin a bubbling fluidized state. A third cyclone 60 is connected to thesecond reduction furnace 30 in order to collect dusty iron orescontained in exhaust gas discharged from the second reduction furnace30.

The drying/preheating furnace 10 is given in a tapered shape beingsmoothly expanded upwards. In details, the drying/preheating furnace 10consists of an enlarged upper cylindrical section 101, an intermediateconical section 102 and a reduced lower cylindrical section 103. Thedrying/preheating furnace 10 is fitted with a first gas inlet 11 at thebottom portion for receiving exhaust gas from the first reductionfurnace 20. Between the conical section 102 and the reduced cylindricalsection 103, a first distributor 12 is installed to evenly distributethe exhaust gas supplied through the first gas inlet 11.

A portion of the side wall of the conical section 102 is fitted with afirst ore inlet 18 through which iron ores are charged from the hopper70 via an ore supply line 71. At another portion of the side wall ofconical section 102 opposite to the portion fitted with the first oreinlet 18, the drying/preheating furnace 10 has a first ore outlet 13 fordischarging the dried/preheated iron ores from the drying/preheatingfurnace 10 and a first dusty ore inlet 15 for receiving dusty iron oreparticles captured by the first cyclone 40.

A first exhaust gas outlet 16 is provided at the upper portion of theenlarged cylindrical section 101. This first exhaust gas outlet 16 isconnected to the first cyclone 40 via a first exhaust gas line 17.

The top portion of the first cyclone 40 is fitted up with a firstcleaned gas discharge line 42 for outwardly discharging cleaned exhaustgas from the first cyclone 40. To the bottom portion of the firstcyclone 40, one end of a first dusty ore discharge line 41 is connected.The other end of the first dusty ore discharge line 41 is connected tothe first dusty ore inlet 15 attached to the conical section 102 of thedrying/preheating furnace 10 so that the dusty iron ores captured by thefirst cyclone 40 is recycled to the drying/preheating furnace 10.

Similarly to the drying/preheating furnace 10, the first reductionfurnace 20 is given in a tapered shape being smoothly expanded upwards.That is, the first reduction furnace 20 consists of an enlarged uppercylindrical section 201, an intermediate conical section 202 and areduced lower cylindrical section 203. The first reduction furnace 20 isalso fitted with a second gas inlet 21 at the bottom portion forreceiving exhaust gas from the second reduction furnace 30. Between theconical section 202 and the reduced cylindrical section 203, a seconddistributor 22 is installed to evenly distribute the exhaust gassupplied through the second gas inlet 21.

At one side wall portion of the conical section 202, the first reductionfurnace 20 has a second ore outlet 23 for discharging iron orespre-reduced in the first reduction furnace 20, and a second ore inlet 28for receiving the dried/preheated iron ore particles from thedrying/preheating furnace 10. At the other side wall portion of theconical section 202, the first reduction furnace 20 has a second dustyore inlet 25 for receiving dusty iron ores captured by the secondcyclone 50.

A second exhaust gas outlet 26 is provided at the upper portion of theenlarged cylindrical section 201. This second exhaust gas outlet 26 isconnected to the second cyclone 50 via a second exhaust gas line 27.

The top portion of the second cyclone 50 is connected to one end of asecond cleaned exhaust gas line 52. To the bottom portion of the secondcyclone 50, a second dusty ore discharge line 51 is connected.

The other end of the second cleaned exhaust gas line 52 is connected tothe first gas inlet 11 attached to the bottom portion of thedrying/preheating furnace 10 in order to supply exhaust gas, whichbecomes free of iron ores in the second cyclone 50, to the drying/preheating furnace 10. The other end of the second dusty ore dischargeline 51 is connected to the second dusty ore inlet 25 attached to theconical section 202 of the first reduction furnace 20 so as that thedusty iron ores captured by the second cyclone 50 is recycled to thefirst reduction furnace 20.

The second ore inlet 28 of the first reduction furnace 20 is connectedto the first ore outlet 13 of the drying/preheating furnace 10 with afirst duct line 14.

Similar to the first reduction furnace 20, the second reduction furnace30 is also given in a tapered shape being smoothly expanded upwards.That is, the second reduction furnace 30 consists of an enlarged uppercylindrical section 301, an intermediate conical section 302 and areduced lower cylindrical section 303. The second reduction furnace 30is also fitted with a third gas supply port 31 at the bottom portion forreceiving exhaust gas from a melter gasifier 80. Between the conicalsection 302 and the reduced cylindrical section 303, a third distributor32 is installed to evenly distribute the exhaust gas supplied throughthe third gas inlet 31.

At one side wall portion of the conical section 302, the secondreduction furnace 30 has a third ore inlet 38 for receiving thepre-reduced iron ores from the first reduction furnace 20. At the otherside wall portion of the conical section 302, the second reductionfurnace 30 has a third dusty ore inlet 35 for receiving dusty iron orescaptured by the third cyclone 60 and a third ore outlet 33 fordischarging iron ores finally reduced in the second reduction furnace30.

At the upper portion of the enlarged cylindrical section 301, the secondreduction furnace 30 has a third exhaust gas outlet 36 which isconnected to the third cyclone 60 via a third exhaust gas line 37.

The top portion of the third cyclone 60 is connected to one end of athird cleaned exhaust gas line 62. To the bottom portion of the thirdcyclone 60, one end of a third dusty ore discharge line 61 is connected.

The other end of the third cleaned exhaust gas line 62 is connected tothe second gas inlet 21 provided at the bottom portion of the firstreduction furnace 20 in order to supply exhaust gas, which become freeof iron ores in the third cyclone 60, to the first reduction furnace 20.The other end of the third dusty ore discharge line 61 is connected tothe third dusty ore inlet 35 provided at the conical section 302 of thesecond reduction furnace 30 so that the dusty iron ores captured by thethird cyclone 60 is recycled to the second reduction furnace 30.

The third ore inlet 38 of the second reduction furnace 30 is connectedto the second ore outlet 23 of the first reduction furnace 20 with asecond duct line 24.

The third ore outlet 33 is connected to the melter gasifier 80 through athird duct line 34 whereas the third gas inlet 31 is connected to themelter gasifier 80 through an exhaust gas line 82.

The bottom portion of the melter gasifier 80 is connected to a pig irondischarge line 81 for discharging pig iron produced by a smeltingreduction operation in the melter gasifier 80.

At the curved or elbow portion of the first duct line 14, a gas supplyport P is installed for supplying a small amount of gas to the firstconduit 14 in order to prevent the conduit 14 from being plugged by ironore particles being fed in the duct line 14. For the same purpose,another gas supply port P is installed at the curved or elbow portion ofthe second duct line 24.

Although the present invention has been described as embodying thereduction apparatus of the three-stage fluidized-bed-type, it may alsobe constructed or modified in the form of a two-stagefluidized-bed-type. The two-stage fluidized bed type reduction apparatushas basically the same construction as that of the three-stage fluidizedbed except that it includes only one reduction furnace which may beeither the first or second reduction furnaces 20 and 30. In this case,iron ore particles dried and preheated in the drying/heating furnace isalmost completely reduced in the single furnace.

Preferably, the conical sections 102, 202 and 302 of thedrying/preheating furnace 10, first reduction furnace 20 and secondreduction furnace 30 have a taper angle ranging from 3° to 25°.

It is also preferred that the conical sections 102, 202 and 302 of thedrying/preheating furnace 10, first reduction furnace 20 and secondreduction furnace 30 have a height 5.0 to 9.0 times as long as the innerdiameter at each lower end. On the other hand, the enlarged sections101, 201 and 301 of the drying/preheating furnace 10, first reductionfurnace 20 and second reduction furnace 30 preferably have a height 2.0to 4.0 times as long as the inner diameter at the upper end of eachcorresponding conical section.

Now, a method for producing reduced iron or molten pig iron using thereduction apparatus of fluidized-bed-type of the present invention willbe described.

As shown in FIG. 2, iron ores contained in the hopper 70 are supplied tothe drying/preheating furnace 10 through the ore supply line 71 andfirst ore inlet 18. The drying/preheating furnace 10 is also suppliedwith exhaust gas from the first reduction furnace 20 through the secondcyclone 50, the second cleaned exhaust gas line 52 and first gas inlet11 in order. This exhaust gas is uniformly dispersed in thedrying/preheating furnace 10 by means of the first distributor 12. Bythe uniformly dispersed gas, the iron ore particles supplied in thedrying/preheating furnace 10 form a bubbling fluidized bed, and aredried and preheated in the fluidized bed. The dried/preheated iron oresare then fed to the first reduction furnace 20 via the first ore outlet13 and first duct line 14.

The exhaust gas is discharged outward from the drying/preheating furnace10, in which iron ores are dried and preheated by the gas before beingexhausted, via the first exhaust gas outlet 16 and first exhaust gasline 17, first cyclone 40 and first cleaned exhaust gas line 42 inorder. Dusty iron ores contained in the exhaust gas are captured by thefirst cyclone 40 and then recycled to the drying/preheating furnace 10via the first dusty ore discharge line 41 and first dusty ore inlet 15.

The dried/preheated iron ores supplied in the first reduction furnace 20are then pre-reduced while forming a bubbling fluidized bed by theexhaust gas which is fed to the first reduction furnace 20 via the thirdcyclone 60, third cleaned exhaust gas line 62, second gas inlet 21 andsecond distributor 22 in order. The pre-reduced iron ores are fed to thesecond reduction furnace 30 via the second ore outlet 23 and second ductline 24.

In the first reduction furnace 20, the exhaust gas from the secondreduction furnace 30 is used for the prereduction of the iron ores andthen discharged from the first reduction furnace 20 via the secondexhaust gas outlet 26 and second exhaust gas line 27, second cyclone 50and second cleaned exhaust gas line 52 in order and then introduced intothe drying/preheating furnace 10. Dusty iron ores contained in theexhaust gas are captured by the second cyclone 50 and then recycled tothe first reduction furnace 20 via the second dusty ore discharge line51 and second dusty ore inlet 25.

Meanwhile, the pre-reduced iron ores supplied in the second reductionfurnace 30 are finally reduced while forming a bubbling fluidized bed bythe exhaust gas which is generated from the melter gasifier 80 andsupplied to the second reduction furnace 30 via the exhaust gas line 82,third gas inlet 31 and third distributor 32. The finally reduced ironores are fed to the melter gasifier 80 via the third ore outlet 33 andthird duct line 34.

The exhaust gas generated from the melter gasifier 80 is at first usedfor the final reduction of iron ore in the second reduction furnace andthen is introduced into the first reduction furnace 20 after beingdischarged through the third exhaust gas discharge port 36 and thirdexhaust gas line 37, third cyclone 60 and third cleaned exhaust gas line6. Dusty iron ores contained in the exhaust gas are captured by thethird cyclone 60 and then recycled to the second reduction furnace 30via the third dusty ore discharge line 61 and third dusty ore inlet 35.

The iron ore particles charged into the melter gasifier 80 is melted,thereby producing molten pig iron (hot metal).

On the other hand, it is preferred that the gas velocity at free boardzone in each of the drying/preheating furnace 10, first reductionfurnace 20 and second reduction furnace 30 is kept within 1.0 to 3.0times the minimum gas velocity required for fluidizing iron oreparticles of the mean grain size staying in the relevant furnace.

For the drying/preheating furnace 10, first reduction furnace 20 andsecond reduction furnace 30, the pressure drop in the furnace preferablyranges from 0.3 to 0.6 atm. and the temperature drop in the furnacepreferably ranges from 30° to 80° C. It is also preferred that thepressure and temperature of gas supplied to the second reduction furnace30 range from 2 to 4 atm. and 800° to 900° C., respectively.

Preferably, the residence time of iron ore particles in each furnace is20 to 40 minutes.

Although the method of the present invention has been described forreducing fine iron ores by use of the three-stage fluidized-bed-typereduction apparatus, it may be also used in a two-stagefluidized-bed-type reduction apparatus for the reduction of fine ironores. As mentioned above, the two-stage fluidized-bed-type reductionapparatus has basically the same construction as that of the three-stagefluidized bed except that it includes only one reduction furnace. In thecase using the two-stage fluidized-bed-type reduction apparatus, ironores dried and preheated in the drying/heating furnace are almostcompletely reduced in the single furnace.

In this case, it is preferred that the gas velocity in free board zoneof either the drying/preheating furnace or single reduction furnace iskept within 1.0 to 3.0 times the minimum gas velocity required forfluidizing iron ore particles of the mean grain size staying in therelevant furnace.

For either the drying/preheating furnace or the single reductionfurnace, the pressure drop occurring in the furnace preferably rangesfrom 0.3 to 0.6 atm. and the temperature drop occurring in the furnacepreferably ranges from 30° to 80° C. It is also preferred that thepressure and temperature of gas supplied to the reduction furnace rangefrom 2 to 4 atm. and 800° to 900° C., respectively.

It is also preferred that the residence time of iron ore particles ineach furnace be 30 to 50 minutes.

As apparent from the above description, each furnace employed inaccordance with the present invention is given a tapered shape, i.e.,the diameter of the furnace increases in the upper direction so as tostably fluidize iron ore particles of wide grain size ranges. With sucha shape, it is possible not only to ensure the fluidization of coarseiron ore particles, but also to more stably fluidize fine iron oreparticles, thereby achieving an efficient reduction of fine iron ores.In accordance with the present invention, the reduction of fine ironores is achieved in multiple stages, for example, three stagescomprising the drying/preheating, first reduction and second reductionstages all having different operations. In accordance with the presentinvention, exhaust gas generated from each furnace is efficiently used,thereby reducing the fuel consumption.

The reason why the reduction of fine iron ores is efficiently carriedout by virtue of the furnace construction according to the presentinvention will now be described in more detail. Since thecross-sectional area of the furnace of the present invention graduallyincreases toward the upper end of the furnace, the gas velocity in thefurnace gradually decreases toward the upper end of the furnace.Accordingly, coarse iron ore particles mostly distributed near thedistributor installed at the lower part of the furnace can be wellfluidized at a high gas velocity. On the other hand, fine iron oreparticles mostly distributed at the upper part of the furnace can beappropriately fluidized at medium/low gas velocity while beingsuppressed so as not to be elutriated. Accordingly, the residence timeof iron ore particles in the furnace can be kept constant irrespectiveof the grain size. Therefore, iron ores of wide grain size ranges can beefficiently reduced while maintaining a stable fluidized state. Thereduction apparatus of the present invention comprisesserially-arranged, multi-stage fluidized-bed-type furnaces, namely, thedrying/preheating furnace for drying and preheating fine iron ores, thefirst reduction furnace for pre-reducing the dried/preheated fine ironores, and the second reduction furnace for finally reducing theprereduced iron ore particles. In this apparatus, exhaust gas generatedfrom each furnace is used as a reducing gas for the preceding reductionstage, thereby increasing the utilization degree of the reducing gas.Therefore, the apparatus and method of the present invention provide aneconomical efficiency of great interest.

The present invention will be understood more readily with reference tothe following example; however this example is only intended toillustrate the invention and is not to be construed to limit the scopeof the present invention.

EXAMPLE

A fluidized-bed-type reduction apparatus having the construction asshown in FIG. 2 was prepared. This fluidized-bed-type reductionapparatus had the following dimension:

    ______________________________________                                        1)  Inner Diameter and Height of Each Fluidized-Bed-                              Type Furnace (Drying/Preheating Furnace, First                                Reduction Furnace and Second Reduction Furnace)                           Inner Diameter of Conical Section at Lower End                                                            0.3 m;                                                                        Height of Conical Section 1.9 m;                                              Inner Diameter of Conical Section at Upper                                    End: 0.7 m;                                                                   Height of Each Cylindrical Section 2.0 m;                                     and                                                                           Taper Angle of Conical Section 6°          ______________________________________                                    

Fine iron ores were then charged into the drying/preheating furnace 10of the fluidized bed type reduction apparatus made as mentioned above,and at the same time a reducing gas was also supplied to the secondreducing furnace 30 through the third gas inlet 31 and third gasdistributor 32 both installed at the second reducing furnace 30.

The fine iron ores were dried and preheated while forming a bubblingfluidized bed by the reducing gas. After being dried and preheated, theiron ores were fed to the first reduction furnace 20, in which theywere, in turn, pre-reduced. After being pre-reduced, the iron ores werefed to the second reduction furnace 30 and then finally reduced. Theiron ores from the second reduction furnace 30 were then fed to themelter gasifier 80. In the melter gasifier, the iron ores were melted.The following conditions were used in the above process:

    ______________________________________                                        2)   Charge and Discharge of Iron Ore Particles                               Composition of Fine Iron Ores                                                  T.Fe: 62.36%, SiO.sub.2 : 5.65%, Al.sub.2 O.sub.3 : 2.91%,                    S: 0.007%, and P: 0.065%;                                                     Particle Size Range                                                           0.25 mm = 22%, 0.25 mm - 1.0 mm = 28%, and                                    1.0 mm - 5.0 mm = 50%;                                                        Feed Rate                                                                     20 Kg/min                                                                     Discharge Rate from Third Ore Discharge Port                                  14.3 Kg/min                                                                  3)   Reducing Gas                                                             Composition      CO: 65%, H.sub.2 : 25%, and                                                    CO.sub.2 + H.sub.2 O: 10%;                                                   Temperature about 850° C.; and                                         Pressure 3.3 Kgf/cm.sup.2                                    4)   Gas Velocity in Each Furnace (Drying/Preheating                               Furnace, First Reduction Furnace and Second                                   Reduction Furnace)                                                       Gas Velocity at Lower End of Conical Section                                                             1.5 m/s; and                                                                  Gas Velocity at Upper End of Conical                                          Section 0.27 m/s                                   ______________________________________                                    

After 60 minutes from the beginning of the reduction, the discharge ofreduced iron started. In this test, the average utilization degree ofthe gas was about 25% whereas the average reduction degree was 87%. Theloss of iron ores caused by the elutriation of dusty iron ores was 0.5%.From this result, it can be concluded that the present invention greatlyreduces the loss of iron ores compared to the conventional cylindricalfluidized bed of which usual loss of iron ores ranges from 8 to 10%.

As apparent from the above description, the present invention, afluidized-bed-type reduction apparatus and a method for reducing ironore particles using the apparatus, is capable of suppressing theelutriation of dusty iron ores in reduction furnaces, thereby reducingthe loss of iron ores as well as increasing the reduction degree. Inaccordance with the present invention, the reduction apparatus comprisesthree fluidized-bed-type furnaces, thereby increasing the utilizationdegree of exhaust gas and reducing fuel consumption.

Although the preferred embodiments of the invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims. For example, although the present invention hasbeen described in conjunction with the two- or three-stagefluidized-bed-type reduction apparatus and reduction method using thisapparatus, it may be applied to reduction apparatus and method capableof reducing iron ore particles in at least four fluidization stages.

What is claimed is:
 1. A fluidized-bed reduction apparatus for reducingiron ore particles, comprising:a drying/preheating furnace for dryingand preheating fine iron ores supplied from a hopper, thedrying/preheating furnace including a first enlarged upper cylindricalsection, a first intermediate conical section and a first reduced lowercylindrical section, the first intermediate conical section having atapered shape being smoothly expanded upwards, the drying/preheatingfurnace further including a first gas inlet provided at a bottom portionof the first reduced cylindrical section, a first distributor installedat an upper portion of the first reduced cylindrical section, a firstore inlet provided at one side wall portion of the first conicalsection, a first ore outlet provided at the other side wall portion ofthe first conical section, a first dusty ore inlet provided at the otherside wall portion of the first conical section, and a first exhaust gasoutlet provided at an upper portion of the first enlarged cylindricalsection; a reduction furnace for finally reducing the fine iron oresdried and preheated in the drying/preheating furnace, the reductionfurnace including a second enlarged upper cylindrical section, a secondintermediate conical section and a second reduced lower cylindricalsection, the second intermediate conical section having a tapered shapebeing smoothly expanded upwards, the reduction furnace further includinga second gas inlet provided at a bottom portion of the second reducedcylindrical section, a second distributor installed at an upper portionof the second reduced cylindrical section, a second ore inlet providedat one side wall portion of the second conical section, a second oreoutlet provided at the one side wall portion of the second conicalsection, a second dusty ore inlet provided at the other side wallportion of the second conical section, and a second exhaust gas outletprovided at an upper portion of the second enlarged cylindrical section;a first cyclone for capturing dusty iron ores contained in an exhaustgas discharged from the drying/preheating furnace and recycling thecaptured dusty iron ores to the drying/preheating furnace whileoutwardly discharging cleaned exhaust gas, free of the dusty iron ores,the first cyclone being connected to the first exhaust gas outlet via afirst exhaust gas line, being connected to the first dusty ore inlet viaa first dusty ore discharge line, and being connected at a top portionthereof to a first cleaned exhaust gas line opened to the atmosphere; asecond cyclone for capturing dusty iron ores contained in an exhaust gasdischarged from the reduction furnace and recycling the captured dustyiron ores to the reduction furnace while supplying cleaned exhaust gas,free of the dusty iron ores, to the drying/preheating furnace, thesecond cyclone being connected to the second exhaust gas outlet via asecond exhaust gas discharge line, being connected to the second dustyore inlet via a second dusty ore discharge line, and being connected tothe first gas inlet via a second cleaned exhaust gas line; a first ductline for connecting the first ore outlet and the second ore inlet sothat the iron ore particles are fed therethrough; a second duct line forconnecting the second ore outlet to a melter gasifier so that the ironore particles are fed to the melter gasifier therethrough; and anexhaust gas line for connecting the second gas inlet to the meltergasifier.
 2. The fluidized-bed reduction apparatus in accordance withclaim 1, wherein the first and second conical sections have a taperedangle ranging from 3° to 25°.
 3. The fluidized-bed reduction apparatusin accordance with claim 1 or 2, wherein the first and second duct linesare provided at their bended portions with gas supply ports forsupplying a small amount of gas to each corresponding duct line.
 4. Thefluidized-bed reduction apparatus in accordance with claim 1 or 2,wherein each of the first and second conical sections has a height 5.0to 9.0 times as long as the inner diameter at the lower end thereof, andeach of the first and second enlarged cylindrical sections has a height2.0 to 4.0 times as long as the inner diameter of each correspondingconical section at the upper end thereof.
 5. The fluidized-bed reductionapparatus in accordance with claim 3, wherein each of the first andsecond conical sections has a height 5.0 to 9.0 times as long as theinner diameter at the lower end thereof, and each of the first andsecond enlarged cylindrical sections has a height 2.0 to 4.0 times aslong as the inner diameter of each corresponding conical section at theupper end thereof.
 6. A fluidized-bed reduction apparatus for reducingiron ore particles, comprising:a drying/preheating furnace for dryingand preheating fine iron ores supplied from a hopper, thedrying/preheating furnace including a first enlarged upper cylindricalsection, a first intermediate conical section and a first reduced lowercylindrical section, the first intermediate conical section having atapered shape being smoothly expanded upwards, the drying/preheatingfurnace further including a first gas inlet provided at a bottom portionof the first reduced cylindrical section, a first distributor installedat an upper portion of the first reduced cylindrical section, a firstore inlet provided at one side wall portion of the first conicalsection, a first ore outlet provided at the other side wall portion ofthe first conical section, a first dusty ore inlet provided at the otherside wall portion of the first conical section, and a first exhaust gasoutlet provided at an upper portion of the first enlarged cylindricalsection; a first reduction furnace for pre-reducing the fine iron oresdried and preheated in the drying/preheating furnace, the reductionfurnace including a second enlarged upper cylindrical section, a secondintermediate conical section and a second reduced lower cylindricalsection, the second intermediate conical section having a tapered shapebeing smoothly expanded upward, the first reduction furnace furtherincluding a second gas inlet provided at a bottom portion of the secondreduced cylindrical section, a second distributor installed at an upperportion of the second reduced cylindrical section, a second ore inletprovided at one side wall portion of the second conical section, asecond ore outlet provided at the one side wall portion of the secondconical section, a second dusty ore inlet provided at the other sidewall portion of the second conical section, and a second exhaust gasoutlet provided at an upper portion of the second enlarged cylindricalsection; a second reduction furnace for finally reducing the fine ironores pre-reduced in the first reduction furnace, the reduction furnaceincluding a third enlarged upper cylindrical section, a thirdintermediate conical section and a third reduced lower cylindricalsection, the third intermediate conical section having a tapered shapebeing smoothly expanded upwards, the second reduction furnace furtherincluding a third gas inlet provided at a bottom portion of the thirdreduced cylindrical section, a third distributor installed at an upperportion of the third reduced cylindrical section, a third ore inletprovided at one side wall portion of the third conical section, a thirdore outlet provided at the other side wall portion of the third conicalsection, a third dusty ore inlet provided at the other side wall portionof the third conical section, a third dusty ore outlet provided at theother side wall portion of the third conical section, and a thirdexhaust gas discharge port provided at an upper portion of the thirdenlarged cylindrical section; a first cyclone for capturing dusty ironores contained in an exhaust gas discharged from the drying/preheatingfurnace and recycling the captured dusty iron ore particles to thedrying/preheating furnace while outwardly discharging cleaned exhaustgas, free of the dusty iron ore particles, the first cyclone beingconnected to the first exhaust gas outlet via a first exhaust gasdischarge line, being connected to the first dusty ore inlet via a firstdusty ore discharge line, and being connected at a top portion thereofto a first cleaned exhaust gas line opened to the atmosphere; a secondcyclone for capturing dusty iron ores contained in an exhaust gasdischarged from the first reduction furnace and recycling the captureddusty iron ores to the first reduction furnace while supplying cleanedexhaust gas, free of the dusty iron ores, to the drying/preheatingfurnace, the second cyclone being connected to the second exhaust gasoutlet via a second cleaned exhaust gas line, being connected to thesecond dusty ore inlet via a second dusty ore discharge line, andconnected to the first gas inlet via a second cleaned exhaust gas line;a third cyclone for capturing dusty iron ores contained in an exhaustgas discharged from the second reduction furnace and recycling thecaptured dusty iron ores to the second reduction furnace while supplyingclean exhaust gas, free of the dusty iron ores, to the first reductionfurnace, the third cyclone being connected to the third exhaust gasoutlet via a third exhaust gas line, being connected to the third dustyore inlet via a third dusty ore discharge line, and being connected tothe second gas inlet via a third cleaned exhaust gas line; a first ductline for connecting the first ore outlet and the second ore inlet sothat the iron ore particles are fed therethrough; a second duct line forconnecting the second ore outlet and the third ore inlet so that theiron ore particles are fed therethrough; a third duct line forconnecting the third ore outlet to a melter gasifier; and an exhaust gasline for connecting the third gas inlet to the melter gasifier.
 7. Thefluidized-bed reduction apparatus in accordance with claim 1, furthercomprising at least one reduction furnace including an enlarged uppercylindrical section, an intermediate conical section and a reduced lowercylindrical section, the intermediate conical section having a taperedshape being smoothly expanded upwards.
 8. The fluidized-bed reductionapparatus in accordance with claim 6, wherein each of the conicalsections has a tapered angle ranging from 3° to 25°.
 9. Thefluidized-bed reduction apparatus in accordance with claim 6, whereinthe first and second duct lines are provided at their bended portionswith gas supply ports for supplying a small amount of gas to eachcorresponding duct line.
 10. The fluidized-bed reduction apparatus inaccordance with claim 6, wherein each of the conical sections has aheight 5.0 to 9.0 times as long as the inner diameter at the lower endthereof, and each of the enlarged cylindrical sections has a height 2.0to 4.0 times as long as the inner diameter of each corresponding conicalsection at the upper end thereof.
 11. The fluidized-bed reductionapparatus in accordance with claim 9, wherein each of the conicalsections has a height 5.0 to 9.0 times as long as the inner diameter atthe lower end thereof, and each of the enlarged cylindrical sections hasa height 2.0 to 4.0 times as long as the inner diameter of eachcorresponding conical section at the upper end thereof.
 12. A method forreducing fine iron ores, comprising the steps of:drying and preheatingthe fine iron ores in a bubbling fluidization state in a fluidized-beddrying/preheating furnace having a tapered shape being smoothly expandedupwards; and finally reducing the dried/preheated iron ores in abubbling fluidization state in a fluidized-bed reduction furnace havinga tapered shape being smoothly expanded upwards.
 13. The method inaccordance with claim 12, wherein the gas velocity at free board zone ofeither the drying/preheating furnace or reduction furnace is kept within1.0 to 3.0 times the minimum gas velocity required for fluidizing ironore particles of the mean grain size staying in the relevant furnace.14. The method in accordance with claim 12 or 13, wherein the pressureof gas supplied to the reduction furnace ranges from 2 to 4 atm., andthe pressure drop occurring in either the drying/preheating furnace orthe reduction furnace ranges from 0.3 to 0.6 atm.
 15. The method inaccordance with claim 12 or 13, wherein the temperature of gas suppliedto the reduction furnace ranges from 800° to 900° C., and thetemperature drop occurring in either the drying/preheating furnace orthe reduction furnace ranges from 30° to 80° C.
 16. The method inaccordance with claim 14, wherein the temperature of gas supplied to thereduction furnace ranges from 800° to 900° C., and the temperature dropoccurring in either the drying/preheating furnace or the reductionfurnace ranges from 30° to 80° C.
 17. The method in accordance withclaim 12 or 13, wherein the residence time of iron ore particles ineither the drying/preheating furnace or the reduction furnace rangesfrom 30 to 50 minutes.
 18. The method in accordance with claim 14,wherein the residence time of iron ore particles in either thedrying/preheating furnace or the reduction furnace ranges from 30 to 50minutes.
 19. The method in accordance with claim 15, wherein theresidence time of iron ore particles in either the drying/preheatingfurnace or the reduction furnace ranges from 30 to 50 minutes.
 20. Themethod in accordance with claim 16, wherein the residence time of ironore particles in either the drying/preheating furnace or the reductionfurnace ranges from 30 to 50 minutes.
 21. A method for reducing iron oreparticles, comprising the steps of:drying and preheating the iron oreparticles in a bubbling fluidization state in a fluidized-beddrying/preheating furnace having a tapered shape being smoothly expandedupwards; pre-reducing the dried/preheated fine iron ores in a bubblingfluidization state in a first fluidized-bed reduction furnace having atapered shape being smoothly expanded upwards; and finally reducing thepre-reduced fine iron ores in a bubbling fluidization state in a secondfluidized-bed reduction furnace having a tapered shape being smoothlyexpanded upwards.
 22. The method in accordance with claim 21, whereinthe gas velocity at free board zone in each of the drying/preheatingfurnace, first reduction furnace and second reduction furnace is keptwithin 1.0 to 3.0 times the minimum gas velocity required for fluidizingiron ore particles of the mean grain size staying in the associatedfurnace.
 23. The method in accordance with claim 21 or 22, wherein thepressure of gas supplied to the second reduction furnace ranges from 2to 4 atm., and the pressure drop occurring in the drying/preheatingfurnace, the first reduction furnace, or the second reduction furnaceranges from 0.3 to 0.6 atm.
 24. The method in accordance with claim 21or 22, wherein the temperature of gas supplied to the second reductionfurnace ranges from 800° to 900° C., and the temperature drop occurringin each of the drying/preheating furnace, the first reduction furnaceand second reduction furnace ranges from 30° to 80° C.
 25. The method inaccordance with claim 23, wherein the temperature of gas supplied to thesecond reduction furnace ranges from 800° to 900° C., and thetemperature drop occurring in each of the drying/preheating furnace,first reduction furnace and second reduction furnace ranges from 30° to80° C.
 26. The method in accordance with claim 21 or 22, wherein theresidence time of iron ore particles in each of the drying/preheatingfurnace, first reduction furnace and second reduction furnace rangesfrom 20 to 40 minutes.
 27. The method in accordance with claim 23,wherein the residence time of iron ore particles in each of thedrying/preheating furnace, first reduction furnace and second reductionfurnace ranges from 20 to 40 minutes.
 28. The method in accordance withclaim 24, wherein the residence time of iron ore particles in each ofthe drying/preheating furnace, first reduction furnace and secondreduction furnace ranges from 20 to 40 minutes.
 29. The method inaccordance with claim 25, wherein the residence time of iron oreparticles in each of the drying/preheating furnace, first reductionfurnace and second reduction furnace ranges from 20 to 40 minutes. 30.The fluidized-bed reduction apparatus in accordance with claim 7,wherein each of the conical sections has a tapered angle ranging from 3°to 25°.
 31. The fluidized-bed reduction apparatus in accordance withclaim 7, wherein the first and second duct lines are provided at theirbended portions with gas supply ports for supplying a small amount ofgas to each corresponding duct line.
 32. The fluidized-bed reductionapparatus in accordance with claim 8, wherein the first and second ductlines are provided at their bended portions with gas supply ports forsupplying a small amount of gas to each corresponding duct line.
 33. Thefluidized-bed reduction apparatus in accordance with claim 7, whereineach of the conical sections has a height 5.0 to 9.0 times as long asthe inner diameter at the lower end thereof, and each of the enlargedcylindrical sections has a height 2.0 to 4.0 times as long as the innerdiameter of each corresponding conical section at the upper end thereof.34. The fluidized-bed reduction apparatus in accordance with claim 8,wherein each of the conical sections has a height 5.0 to 9.0 times aslong as the inner diameter at the lower end thereof, and each of theenlarged cylindrical sections has a height 2.0 to 4.0 times as long asthe inner diameter of each corresponding concial section at the upperend thereof.
 35. The fluidized-bed reduction apparatus in accordancewith claim 31, wherein each of the conical sections has a height 5.0 to9.0 times as long as the inner diameter at the lower end thereof, andeach of the enlarged cylindrical sections has a height 2.0 to 4.0 timesas long as the inner diameter of each corresponding conical section atthe upper end thereof.
 36. The fluidized-bed reduction apparatus inaccordance with claim 32, wherein each of the conical sections has aheight 5.0 to 9.0 times as long as the inner diameter at the lower endthereof, and each of the enlarged cylindrical sections has a height 2.0to 4.0 times as long as the inner diameter of each corresponding conicalsection at the upper end thereof.